Tunable High-Order Multi-Band Bandpass Filters Using Transversal Multi-Resonant Cells

This paper reports on the design of tunable high-order multi-band bandpass filters (BPFs). The proposed concept lays its foundations on series-cascaded multi-band stages, each of them shaped by two identical transversal multi-resonant cells. The transfer function characteristics of each band are tuned by a pair of resonators in each cell that control the center frequency, bandwidth (BW), and mode of operation—bandpass or all-reject—. The overall BPF exhibits a multi-band transfer function with 1-to-N bands that can be independently tuned in terms of frequency, BW, and number. The operating principles of this multi-passband filter concept are demonstrated through simulated examples of a quad-band BPF and the measurement of a tri-band microstrip prototype.